diff --git a/src/serbb_posix.c b/src/serbb_posix.c
index 868ec21e..b4306df1 100644
--- a/src/serbb_posix.c
+++ b/src/serbb_posix.c
@@ -62,11 +62,11 @@ static struct termios oldmode;
 
 #define DB9PINS 9
 
-static int serregbits[DB9PINS + 1] =
+static const int serregbits[DB9PINS + 1] =
 { 0, TIOCM_CD, 0, 0, TIOCM_DTR, 0, TIOCM_DSR, TIOCM_RTS, TIOCM_CTS, TIOCM_RI };
 
 #ifdef DEBUG
-static char *serpins[DB9PINS + 1] =
+static const char *serpins[DB9PINS + 1] =
   { "NONE", "CD", "RXD", "TXD", "DTR", "GND", "DSR", "RTS", "CTS", "RI" };
 #endif